"death," 1869, a euphemistic verbal noun from pass (v.) in such Middle English phrases as passing of death, passing of the soul (c. 1300). A passing-bell (1520s) was a church bell tolled at the time of a person's death.
mid-14c., "transitory;" late 14c., "going by," present-participle adjective from pass (v.). Also from late 14c. as "surpassing, excellent," and "casual, superficial, cursory, as though done in passing." Related: Passingly.